The invention relates to an arrangement for manufacture of voluminous products made of plastics and of rubber compounds.
For injection of structural foam, i.e. of plastics with expansive character, which provide in a mould an integral moulding with a porous core and a compact surface, a number of particular manufacturing processes and especially adjusted arrangements are used at present. The expansion of the melt is achieved by a foaming agent introduced into the mould together with the melt. The foaming agent can be some material decomposing at elevated temperature, for instance azodicarbonamide and similar or compressed gas, for instance nitrogen.
The thus prepared melt is injected into the mould at elevated speed either by means of a piston from a storage chamber after its filling by a plastic injecting worm or directly by an axial motion of the face of the plastic injecting worm from the plastic injecting chamber.
Arrangements for injection of the material from a storage chamber have this chamber situated so that the motion of the piston is either parallel, concurrent or perpendicular to the axis of the mould, which itself is perpendicular to clamping plates. In case the injection is carried out perpendicularly to the axis of the mould, the chamber terminates advantageously in a nozzle parallel with the axis of the mould and bearing against a lateral wall of the mould. The mould is in direction of its partition plane provided with an inlet, whereby the melt proceeds from one side of the hollow space to the other. This arrangement and process are used in case of a perpendicular arrangement of the injection unit to one or more closures, for instance at a closure with a vertical axis, where the surface of the extension is horizontal and the injection is carried out from the lateral side of the press. Another arrangement has an outlet situated in the axis of the chamber.
The outlet is at its end forked so that both its ends fill the mould in the direction of its axis. Universal arrangements for injection of structural foam and classical plastics are solved so that a hydraulic accumulator with the respective distributing means is connected to currently manufactured classical machines. By this arrangement the original high injection pressure is maintained and the speed of the injection i.e. the motion of the worm is increased, but the maximum volume which could be originally injected is not increased.
The described known arrangements using a chamber with an injection piston are designed solely for injection by low pressure technology as their chambers are designed for low injection pressures and larger volumes. The chambers are also, when compared with arrangements for injection of classical homogenous extensions, connected to closing units with low closing forces and weak posts.
With current arrangements for high pressure injection of classical materials also with foaming agents, operating at high speed and pressure, the magnitude of extrusions is limited solely by the capacity of the injection unit. The magnitude of these extrusions is equal to current extrusions of classical materials.
Due to the diversity of molded articles, particularly of their weight and dimensions, the full size of clamping plates and the available opening of the molding machine, molding machines cannot be fully utilized to accommodate a wide variation of molding requirements. The installation of single purpose machines is frequently not economical, and the machines cannot be fully utilized.
Where rapid setup for low cost manufacture of structural plastic foams with large extrusion volume must be placed in current manufacture, great difficulties are presently experienced due to time lags and particularly due to impractically high costs involved therein.
A substantial drawback of known arrangements is that for extrusions of not foamed materials the manufacture of larger products surpassing the capacity of the machine is impossible.
The manufacture of two component sandwich products by injection with a compact surface layer and a foamed core is at present limited to special macnhines with two injection units.
The actually used injection units beyond the proper closing unit as an additional device requires due to its length and weight large spaces in order that the injection nozzle could reach the circumference of the mould.
Low pressure injection units for structural foams which enable a manufacture of products of large size cannot be used for high pressure injection of foamed material as they do not enable extrusions with smooth surfaces.
The individual described arrangements of machines have the following characteristic features limiting their universal technological application.
at constructions of closures for low closing forces a limitation for low injection pressures;
at two component injection, complicated injection units both from the point of view of hydraulic circuitry and of electrical control circuits and availability of space;
at solutions with an additional injection chamber with a piston, this chamber is provided instead of the original plastic injecting worm injection cylinder, which is removed to another place and in construction adapted as a simple plastic injecting worm cylinder without an axial motion of the worm.
if the original construction of the injection unit with the plastic injecting worm cylinder in the axis of the mould is retained, this plastic injecting cylinder has no worm with an axial motion and the injection cylinder with a piston controlled by a hydraulic cylinder has its proper drive and control, whereby the plastic injecting cylinder and the injection mould are connected via some special distributing means.